Abstract Purkinje neurons, the principal projection neurons of the cerebellar cortex, fire high frequency action potentials in the absence of synaptic input. Voltage-gated calcium (Ca) and calcium-activated potassium (KCa) channels contribute to the regularity of this spontaneous activity. Ca channel mutations can cause a number of genetic disorders, including both episodic and spinocerebellar ataxias, as well as familial hemiplegic migraine. Thus, studying Ca and KCa channel physiology has the potential to increase our understanding of the pathology underlying several different disease states. Our recent work has shown that during spontaneous firing, Purkinje cell Ca currents are remarkably stable in amplitude. This feature distinguishes them from many neurons throughout the brain, in which sustained high-frequency activity causes Ca currents to both facilitate and inactivate, resulting in significant changes in the amount of Ca that enters the cell during an action potential. Importantly, Purkinje cell Ca currents have the capacity for modulation, but facilitation and inactivation are balanced. In our proposed experiments, we will examine how two downstream targets of Ca influx, the big (BK) and small (SK) conductance KCa channels, respond to high-frequency stimulation. We will make whole cell voltage clamp recordings from dissociated mouse Purkinje neurons and test whether BK and SK currents filter or amplify the small changes in the Ca currents. Next, we will measure the amplitude and kinetics of these currents when activated by the cells'own action potential waveform. Finally, we will examine SK currents in the leaner mouse, which has a mutant Ca channels and is ataxic. Together, these data will help us to understand how Ca signaling shapes the normal activity of Purkinje cells, and by extension, how disruptions lead to disease. ) PUBLIC HEALTH RELEVANCE: This project examines the cellular mechanisms underlying electrical activity in Purkinje cells of the cerebellum, a region of the brain important for motor coordination. Genetic mutations can cause these neurons to behave abnormally, which is thought to cause multiple forms of ataxia. Our goal is to understand how the electrical activity in Purkinje neurons is regulated, which promises to provide insight into therapeutic treatments for cerebellar disorders.)